1. Field of the Invention
The present invention relates to a disc drive for playing back or recording and playing back an optical disc.
2. Description of the Prior Art
One example of a disc drive for playing back an optical disc such as a CD-ROM or the like is disclosed in Japanese Utility Model Application No. HEI-5-69414. FIG. 1 is an exploded perspective view of the structure of the disc drive disclosed in the Utility Model application.
As shown in this drawing, a disc drive 1B is constructed from a main body 2B, a disc tray 4 which moves backwards and forwards with respect to the main body 2B to enable the disc tray 4 to be insertable into and ejectable out of the main body 2B, a circuit substrate assembly 12B arranged at a lower portion of the main body 2B, and a casing 10B which houses all these elements.
The casing 10B is constructed from a bottom plate 11 and a case 14 which covers the top of the main body 2B. The bottom plate 11 and the case 14 are made from metal plates which have undergone cutting and bending processes to form a desired shape.
The case 14 is constructed from a top plate 14a, side walls 14b, 14c which face each other through the main body 2B, a rear wall 14d which connects the rear vertical edges of the side walls 14b, 14c, and a front plate portion 14e at the front thereof.
Provided on the bottom surface (inside surface) of the top plate 14a is a disc clamper 38 which is adapted to rotate about the same axis as that of a turntable 26 (described below).
Formed in the front plate 14e of the case 14 is an aperture 14 which allows the disc tray 4 to be passed therethrough. A front panel 16 having an aperture 16a which is mated with the aperture 141 is mounted on the front plate 14e via a cushioning member frame 15.
The main body 2B includes a roughly container-shaped chassis 20 which is provided with a mechanism unit 22 and a displacement mechanism (ascending/descending mechanism) 30. The mechanism unit 22 is arranged within a concave portion formed in the bottom portion 20a of the chassis 20, and the displacement mechanism 30 is arranged in the front side thereof.
The main body 2 is fixed to the bottom plate 11 and the case 14 by means of screws 17.
The mechanism unit 22 includes a base 23 which is provided with a spindle motor 25, a turntable 26 which is provided on a rotation axle of the spindle motor 25, an optical head 27, and an optical head moving mechanism 28.
Further, a rear end portion (toward the back of the main body 2) of the base 23 is supported by an insulator 29 to enable the base 23 to be freely pivotal with respect to the chassis 20.
The displacement mechanism 30 is constructed from a motor 31 provided at a front portion of the chassis 20, a rotational speed reduction mechanism 32 for reducing the rotational speed of the motor 31, a cam wheel (ascending/descending gear member) 33 which is rotated by the rotational speed reduction mechanism 32, and a base ascending/descending member (not shown in the drawing) which is adapted to be displaced (rotated) in accordance with the rotation of the cam wheel 33.
The cam wheel 33 includes a lower gear 33a which meshes with a pinion gear of the rotational speed reduction mechanism 32, and an upper gear 33b which meshes with a rack gear (not shown in the drawing) formed on the bottom surface of the disc tray 4 in the forward and backward direction thereof. Further, a circumferential cam groove is formed in the outer circumference of the axle portion between the gears 33a and 33b. This cam groove is slidably engaged with a protruding follower (not shown in the drawing) formed on the base ascending/descending member. Consequently, as the cam wheel is rotated, the follower and the base ascending/descending member are displaced, and this causes the base 23 to pivot; namely, the front portion of the base 23 is moved up or down.
The disc tray 4 includes a shallow concave disc supporting portion 4a for supporting an optical disc 3. On the bottom surface of the disc tray 4, there is is formed a rack gear (not shown in the drawing) which meshes with the upper gear 33b of the cam wheel 33. Consequently, as the cam wheel 33 is rotated, the disk tray 4 is moved forward or backward with respect to the chassis 20 between a disc unloading position (outside position) and a disc loaded position (inside position).
When the disc drive 1B is not in use, the disc tray 4 is housed within the casing 10B (at the disk loaded position). In this state, if an eject operation is carried out, the motor 31 is rotated in a prescribed direction, whereby the cam wheel 33 is rotated in a prescribed direction via the rotational speed reduction mechanism 32. This rotation of the cam wheel 33 causes the disc tray 4 to move forward so that the disc tray 4 protrudes to a position (the disc unloading position) outside the casing 10B through the apertures 141, 16a.
In this state, a disc 3 is loaded or put into the disc supporting portion 4a of the disc tray 4, and a loading operation is carried out, whereby the motor 31 is rotated in the opposite direction. This causes the cam wheel 33 to rotate in the opposite direction via the rotational speed reduction mechanism 32. Consequently, the disc tray 4 is moved backwardly, through the apertures 141, 16a, to the disc loaded position. In this way, the loaded optical disc 3 which is placed at a prescribed position on the disc tray 4, that is placed in the disc supporting portion of the disc tray 4 is also transported to the disc loaded position of the main body 2B.
Further, when the cam wheel 33 begins to rotate in the opposite direction, the follower of the base ascending/descending member moves along the cam groove. When the center of the disc 3 supported on the disc tray 4 approaches the central portion of the turntable 26 according to the rotation of the cam wheel 33, the follower and the base ascending/descending member are displaced by the cam wheel 33 so that the front portion of the base 23 pivots about the position of the insulator 29 to displace the front portion of the base 23 from a lower position (descending position) to an upper position (ascending position), whereby the base 23 is placed in a roughly horizontal state.
In this way, the center portion (center hub portion) of the turntable 26 is fitted into a center hole 3a of the optical disc 3. When the center portion of the optical disc is supported on the turntable 26 in this way, the disc damper 38 is magnetically stuck to the turntable 26, thereby the optical disc 3 being held between the turntable 26 and the disc clamp 38. In this state, the spindle motor 25 is operated to rotate the optical disc 3 at a predetermined rotational speed, and then the information recorded on the optical disc 3 is played back using the optical head 27.
If an eject operation is carried out while the rotation of the optical disc 3 is stopped, the order and direction of the operations of each mechanism of the disc drive 1B are carried out in reverse, so that the clamp of the disc 3 is released and then the optical disc 3 placed on the disc tray 4 is ejected.
In recent years, in the field of the disc drives like the disc drive 1B described above, developments are made in order to increase a rotational speed of an optical disc. As a result, disc drives which can rotate an optical disc 3 at high speeds, such as 8 times speed, 12 times speed and the like are developed, but this in turn arises the following problems.
The allowable dimensional error range of the optical disc 3 is determined according to a standard, however such standard was prepared based on the basic rotational speed of the optical disc 3, that is 1 times speed. For this reason, when such an optical disc 3 is driven at a high speed (i.e., a speed which exceeds 1 times speed), vibration is likely to occur due to eccentric rotation caused by the dimensional deviation of the disc and the unbalanced distribution of mass of the optical disc 3 which lie in the range allowed by the standard. Further, more severe vibration will occur in the case where the optical disc 3 was not manufactured according to the standard (i.e., an inferior product).
Further, this type of vibration will also occur if the axes of the optical disc 3 and the turntable 26 are misaligned (i.e., eccentrical).
Unfortunately, an effective countermeasure for suppressing such vibration has not been adopted in such a prior art disc drive 1B described above. In particular, because the main body 2B is fixed to the metal bottom plate 11 and the metal case 14 by means of the screws 17, as described above, vibrations caused by eccentric rotation of the optical disc 3 or the like are easily transmitted from the main body 2B to the metal casing 10B, which causes the casing 10B to resonate and thereby generate noise.
Also, in the case where the disc drive is installed in a personal computer, such vibrations are also transmitted to the personal computer body, thereby creating unfavorable effects to the personal computer. Further, in the other direction, vibrations from the personal computer are also transmitted to the disc drive.
In order to prevent such vibration and noise from being generated, it may be possible to adopt a structure in which a plurality of coil springs are arranged between the lower plate 11 and the main body 2B so that the main body 2B are supported by such coil springs to absorb vibrations, but this in turn creates the following problems.
Namely, although the above-described structure is suited for absorbing vibration in the vertical direction (i.e., the rotational axial direction of the optical disc), most of the vibrations which are generated in the main body 2 occur in the horizontal direction (i.e., the radial direction of the optical disc) because they are caused by the eccentric rotation of the optical disc 3. Therefore, it is not possible to obtain a sufficient vibration absorbing (damping) and noise preventing effects (damping effect). Also, such damping effect is affected by the posture of the disc drive, namely affected by the posture of the PC equipped with the disc drive whether it is placed horizontally or vertically.
Further, because the coil springs in the above structure are provided in the lower portion of the main body 2B, it is not possible to make effective use of the space of such portion.
Furthermore, because the vibration absorbing coil springs need to be fixed from the rear side of the bottom plate 11 with screws, number of parts are increased.
In addition, as stated in the above, the vibration described above is transmitted from the main body 2B to the metal casing 10B (bottom plate 11 and case 14), thereby causing the casing 10B to resonate and generate noise. Such noise is generated due to the reason stated below.
Namely, in the construction of the prior art disc drive, the lower edges of the side walls 14b, 14c and the rear wall 14d of the case 14 are in abutment with the inner surface of the bottom plate 11 directly. However, the lower edges of the side walls 14b, 14c and the rear wall 14d of the case 14 have lower linear precision, since they are formed by carrying out a shearing process on a metal plate using a press machine or the like and no later shape correction such as a precision process or the like is carried out. Therefore, there are many irregularities on the edges and the linear precision of the edges is bad. For this reason, when the case 14 and the bottom plate 11 are assembled, even when these elements are tightly fixed using screw fasteners, the connection between the bottom plate 11 and each lower edge of the side walls 14b, 14c and rear wall 14d is unstable.
In such an unstable connected state, when vibration is transmitted to the casing 10B as described above due to high speed rotation, a rattling is created between the case 14 and the bottom plate 11, thus generating an even greater amount of noise.